This invention relates generally to radiographic inspection and more particularly to high speed digital radiography for inspecting aircraft fuselages.
An aircraft fuselage typically comprises a grid of circumferential frame members and longitudinal stringers covered by a skin of lightweight sheet metal. The skin is ordinarily attached to the frame members and stringers by means of rivets or the like. To ensure passenger comfort at high altitudes, aircraft are provided with cabin pressurization systems that produce near sea-level air pressure breathing environments in the aircraft cabin. The application of cabin pressure causes the skin, frame members and stringers to expand slightly. When the pressure is removed, the skin, frame members and stringers return to their normal shape. Although the pressure differentials involved are relatively small, the repeated cycles of stress imposed on the fuselage structure by the pressurization and depressurization sequence that occurs during each flight can lead to fatigue and crack formation. This fatigue damage is often assisted by corrosion of the fuselage structures.
Fatigue cracks by nature can be extremely small in size and difficult to detect. The cracks are normally so small that routine pressurization of the aircraft cabin will not result in detection because the tiny cracks will not cause a detectable pressure loss in the aircraft. The combined effect of corrosion and cyclic stress can also cause looseness around the rivets and/or rivet cracking. If not detected, this condition could result in skin separation from the frame members and stringers.
Traditionally, aircraft fuselage inspection relies largely on visual inspection techniques. These techniques require extensive disassembly of the aircraft, including removal of objects such as overhead bins, interior panels, insulation and the like. This approach is thus time consuming, labor intensive and expensive. Furthermore, visual inspection techniques rely heavily on human ability and are limited by ambient lighting conditions, environmental effects, and the inspector""s physical and mental limitations such as eye vision corrections, time constraints, mental attitude, concentration and judgment.
Radiography is another approach to aircraft fuselage inspection that has been proposed. However, using radiographic film to capture images of the fuselage is a costly, labor intensive process typically requiring large amounts of film. It is also a relatively slow process as the film must be removed and developed before the images can be examined. Replacing the film with an X-ray detector capable of providing electronic images is an alternative to X-ray film, but systems of this sort generally require precise alignment of the X-ray source and detector with respect to each other and the fuselage. This alignment has been heretofore difficult to achieve given the immense size of aircraft fuselages.
Accordingly, it would be desirable to have a method and apparatus capable of performing high speed digital radiographic inspection of aircraft fuselages without removal of interior bins, panels, insulation, lights, wiring and so on.
The above-mentioned need is met by the present invention, which provides a system and method for radiographic inspection of aircraft fuselages in which a radiation source is preferably located inside of the fuselage, and a radiation detector is preferably located outside of the fuselage. A source positioning system is provided for moving the radiation source longitudinally with respect to the fuselage, and a detector positioning system is provided for positioning the radiation detector in longitudinal alignment with the radiation source. The detector positioning system also moves the radiation detector circumferentially with respect to the fuselage. In operation, the radiation detector is moved over the fuselage in a circumferential direction while the radiation source illuminates an adjacent region of the fuselage with radiation.
The present invention and its advantages over the prior art will become apparent upon reading the following detailed description and the appended claims with reference to the accompanying drawings.